Lithographic etching solution



Patented Jan. 28, 1941 UNITED STATES PATENT OFFICE 7 2,230,156 LITHOGRAPHIC ETCHING SOLUTION Everett F.

Inter-chemical Corpora I corporation of Ohio Carman, Rutherford, N. J., assignor to Hon, New York, N. Y., a

No Drawing Application March 6, 1940,

Serial No. 322,573

2 Claims.

This invention relates to etching solutions for lithographing plates, and is particularly directed to etching solutions which attack chromium but not copper or conventional exposed bichromated coatings used to prepare lithographic plates.

There has recently been developed a new printing plate, comprising a grained coppered printareas. In

ing surface covered with a thin coating of water-receptive chromium in j the non-printing the preparation of such plates,- a

, grained copper plate is coated with chromium,

or polyvinyl alcohol and a bichromated'solution oi gelatin, gum arabic is coated over the chromium. The sensitized coating is then exposed to light through a suitable positive, and the undeveloped coating removed, leaving the chromium bare in the printing portions. The chromium may be etched by any chemical solution which dissolves chromium but which does not attack the copper. However, the ordinary aqueous solutions of chemicals tend to attack the developed coating as well, particularly in halitone structures, where the coating may exist only as an isolated dot. As a result, the ordinary aqueous chemical solutions can be used only toproduce line prints, and are not satisfactory for half tones. I have discovered etching solutions which make possible the etching of chromium while avoiding any attack on copper, or on exposed bichromated gelatin, gum arabic or polyvlnyl'alcohol. These solutions comprise mixtures of .aqueous hydrochloric acid with completely water miscible glycol containing more carbon atoms thanhydroxyl groups, using between about 3 to Mix 6 parts of glycol by volume to 1 part of concentrated aqueous acid (37%). The typical glycols of this type include diethylene glycol, propylene glycol, and dipropylene glycol.

-Typical examples of my invetnion are the following:

Example 1 -3 volumes of propylene glycol with 1 volume of 37% hydrochloric acid v Example 2 6 volumes of diethylene glycol with 1 volume of 37% hydrochloric acid hi'caniple 3 3 volumes of diproplene glycol with 1 volume of 37% hydrochloric acid 

